The objectives of this proposal are to study certain relationships between pulmonary function and airway structure. Particular emphasis will be placed on marine mammals and other marine aquatic vertebrates (excluding fish), although certain terrestrial species will be studied for comparative purposes. The interest in the marine forms is because they have peculiar modifications of their lungs which must be related to immersion and compression. Using pressure as a tool and taking advantage of the breath-hold ability of the aquatic animals will enable us to study in a unique way some of these pulmonary modifications. Those problems to be studied are: 1) the mechanical properties of the lungs in vitro and in vivo, 2) the influence of lung volume and airway structure on pulmonary gas exchange at 1 atm. and various hydrostatic pressures, 3) the problems of re-expanding atelectatic lungs, and 4) methods of ventilation in various species and the correlation with expiratory peak flow measurements. These studies are related to the clinical problems of chronic obstructive lung disease. This work will be a collaborative effort between Scripps Institution of Oceanography and the University of California, San Diego, School of Medicine.